ABSTRACT
Although recognition of lipopolysaccharide (LPS) by the myeloid differentiation factor 2-Toll-like receptor 4 complex is important for triggering protective inflammatory responses in animals, terminating many of these responses requires LPS inactivation by a host lipase, acyloxyacyl hydrolase (AOAH). To test whether endogenously produced recombinant AOAH can modulate responses to LPS and gram-negative bacteria, we engineered transgenic mice that overexpress AOAH in dendritic cells and macrophages, cell types that normally produce it. Transgenic mice deacylated LPS more rapidly than did wild-type controls. They also were protected from LPS-induced hepatosplenomegaly, recovered more quickly from LPS-induced weight loss, and were more likely to survive when challenged with live Escherichia coli. Constitutive overexpression of AOAH in vivo hastened recovery from LPS exposure without interfering with the normal acute inflammatory response to this important microbial signal molecule. Our results suggest that the extent to which macrophages and dendritic cells produce AOAH may influence the outcome of many gram-negative bacterial diseases.
Subject(s)
Carboxylic Ester Hydrolases/biosynthesis , Dendritic Cells/enzymology , Lipopolysaccharides/pharmacology , Macrophages, Peritoneal/enzymology , Animals , Antibodies, Monoclonal/pharmacology , Antigens, CD/biosynthesis , Antigens, CD/genetics , Antigens, Differentiation, Myelomonocytic/biosynthesis , Antigens, Differentiation, Myelomonocytic/genetics , Carboxylic Ester Hydrolases/genetics , Carboxylic Ester Hydrolases/immunology , Dendritic Cells/immunology , Enzyme Induction/drug effects , Gram-Negative Bacterial Infections/enzymology , Gram-Negative Bacterial Infections/immunology , Hepatomegaly/chemically induced , Lipopolysaccharides/immunology , Lipopolysaccharides/pharmacokinetics , Liver/drug effects , Liver/enzymology , Macrophages, Peritoneal/immunology , Mice , Mice, Inbred C57BL , Mice, Transgenic , Promoter Regions, Genetic , RNA, Messenger/metabolism , TransfectionABSTRACT
Much of the inflammatory response of the body to bloodborne Gram-negative bacteria occurs in the liver and spleen, the major organs that remove these bacteria and their lipopolysaccharide (LPS, endotoxin) from the bloodstream. We show here that LPS undergoes deacylation in the liver and spleen by acyloxyacyl hydrolase (AOAH), an endogenous lipase that selectively removes the secondary fatty acyl chains that are required for LPS recognition by its mammalian signaling receptor, MD-2-TLR4. We further show that Kupffer cells produce AOAH and are required for hepatic LPS deacylation in vivo. AOAH-deficient mice did not deacylate LPS and, whereas their inflammatory responses to low doses of LPS were similar to those of wild type mice for approximately 3 days after LPS challenge, they subsequently developed pronounced hepatosplenomegaly. Providing recombinant AOAH restored LPS deacylating ability to Aoah(-/-) mice and prevented LPS-induced hepatomegaly. AOAH-mediated deacylation is a previously unappreciated mechanism that prevents prolonged inflammatory reactions to Gram-negative bacteria and LPS in the liver and spleen.
